The gutting process in the kitchen, and ripping down the tin ceiling (not original) revealed a hole in the ceiling as well as some rusting. This also exposed a leaking problem from the bathroom. After some investigation and a decision to immediately gut the upstairs bathroom the problem was revealed. The drain pipe led to a drum drain which backed up and overflowed through a crack in the drain pipe.

Also... the tile was porous. The lathe and plaster, as you can see in the below picture, were saturated due to a fail in the grout around the tile. Clearly when the previous owners "re-bathed" the cast iron tub last February it contributed to an already established weakness in the drain and the tile. Luckily it seems the leaking had only been going on for about that period of time and had not yet undermined the structural integrity of the bathroom superstructure.